Self-piercing and clinching female fasteners such as nuts were developed by the predecessor in interest of the Applicant (Multifastener Corporation) about 50 years ago as disclosed for example in U.S. Pat. No. 2,707,322. Self-piercing and clinching nuts are attached to a metal panel in a die press which may also be used to simultaneously form the panel, wherein generally the upper die platen includes an installation head and the lower die platen includes a die member or die button. Such self-piercing and clinching nuts include a projecting pilot portion which pierces an opening in the panel and the panel metal adjacent the pierced panel opening is then clinched to the fastener with each stroke of the die press.
More recently, self-piercing and clinching male and female fasteners were developed having a tubular barrel portion as disclosed, for example, in U.S. Pat. No. 4,555,838 assigned to the assignee of this Application. The self-piercing and clinching fasteners disclosed in this patent include a tubular barrel portion and a radial flange portion. Such self-attaching male fasteners are installed in a die press, as described above, wherein the lower die platen includes a die button having a panel supporting surface, a central die post and an annular die cavity surrounding the die post. The annular die cavity includes a semicircular annular bottom surface, a radial lip portion at the upper extent of the semicircular bottom surface and a generally frustoconical surface extending from the radial lip portion to the end surface of the die button. In the embodiment disclosed in this patent, the generally frustoconical upper die surface includes a plurality of flats which extend from the annular lip to the end or bearing face of the die button which provide anti-rotation means by drawing and slightly deforming the flange of the stud fastener. It is very important in most applications of the self-piercing and riveting male fasteners that the fastener be able to withstand significant torque loads without twisting in the panel which may destroy the fastener and panel assembly. It was found, however, that the anti-rotation means disclosed in this patent was insufficient for many applications, including automotive applications.
Various attempts have been made to improve the torque resistance of self-piercing and riveting stud fasteners of the type disclosed in U.S. Pat. No. 4,555,838. Initially, anti-rotation protrusions or nubs were provided either on the barrel portion, adjacent the body portion, or on the flange portion adjacent the barrel portion as disclosed, for example, in U.S. Pat. No. 4,810,143, also assigned to the assignee of the present Application. Presently, self-attaching stud fasteners of the type disclosed herein include a plurality of spaced pockets in the outer edge of the flange portion adjacent the barrel portion as disclosed in U.S. Pat. No. 5,020,950, also assigned to the assignee of the present Application. There remains, however, several problems associated with the use of pockets in the flange portion as disclosed in U.S. Pat. No. 5,020,950. First, the die surfaces which form the pockets wear, such that the pockets are not always fully formed in the flange portion resulting in insufficient torque resistance. Second, the self-piercing stud fastener and panel assembly is press sensitive. That is, if the panel metal is not fully deformed into the pockets, the torque resistance will be inadequate. Further, the pockets form stress risers in the panel which can become a source of failure of the fastener and panel assembly. Finally, the use of pockets in the flange portion may provide insufficient torque resistance, particularly where extreme torque resistance is required.
There are also other problems associated with self-piercing and clinching fastener installations of the type disclosed herein which are addressed by the improved fastener, method of installation and die member of this invention. First, the flange portion which surrounds the bolt or stud portion in a male fastener for example is deformed both radially and axially relative to the stud portion by the annular plunger of the installation head which drives the self-piercing and clinching fastener into the panel and the die button, particularly where the press setting is greater than required for installation. This is because the flange portion bottoms against the panel in the die button during installation. As best described in the above-referenced U.S. Pat. No. 4,555,838, the panel metal adjacent the pierced panel opening bottoms on the radial lip of the die button and is then driven into the U-shaped end portion formed in the free open end of the barrel portion. Second, the installation of the self-piercing fastener in a panel is press sensitive. That is, if the press does not provide sufficient force for full installation, the fastener will be loose in the panel providing insufficient pull-out strength and torque resistance. Alternatively, in an “overhit” condition of the die press, the flange portion will be deformed by cold working as previously described. However, even where the fastener is properly installed in the panel with the preferred die setting, the torque resistance may be insufficient, as described above, or the stud or bolt may provide insufficient resistance to tilting in the panel assembly. Finally, the die button is relatively complex and therefore expensive to manufacture and has a relatively poor die life, particularly where the die button is utilized to install self-piercing fasteners of the type described herein in relatively high strength metals, such as HSLA steel. It would therefore be desirable to provide improved torque resistance, eliminate deformation or cold working of the flange portion, reduce sensitivity to die press settings and reduce the cost of the die button, while improving die life.
As described below, the preferred embodiment of the self-piercing and attaching fastener utilized in the method of installation preferably includes a plurality of spaced arcuate radially inwardly concave surfaces or arcuate scallops in the outer side surface of the flange portion. U.S. Pat. No. 6,122,816, assigned to the assignee of the present application, discloses a self-riveting stud fastener including a tubular barrel portion and a radial flange portion having a plurality of spaced arcuate radially inwardly concave surfaces on the outer surface of the flange portion which provide torque resistance and the barrel portion has a conical outer surface developed for installation in thicker panels having a preformed panel opening. Thus, the method of installation disclosed in this patent preferably includes preforming a panel opening and driving of the barrel portion through the panel opening into a semicircular annular die cavity which deforms the free end of the barrel portion into generally a U- or C-shape as disclosed. Continued driving of the flange portion with an annular plunger or punch then drives the flange portion into the panel, cutting and deforming the panel into the shape of the concave and convex surfaces, providing improved torque resistance.
However, the method of installation disclosed in U.S. Pat. No. 6,122,816 has many of the same problems described above in regard to the present method of installing a self-piercing fastener, including press sensitivity and deformation or cold working of the flange portion, particularly in an “overhit” setting of the press. It is possible to actually shear the flange portion from the barrel or body portion in an overhit condition. As the flange portion is driven into the panel by the method disclosed in this patent, the scalloped flange cuts into the panel forming stress risers particularly at the convex edges between the arcuate concave surfaces or flutes, reducing the integrity of the joint. Further, the panel metal under the flange is compressed, causing deformation of the bearing surface at the top of the flange.